1. Field of the Invention
The present invention relates to an image-shake correcting device for optically correcting an image shake resulting from unexpected vibrations by driving a part of a photo-taking optical system.
2. Description of Related Art
Image-shake correcting devices have heretofore been arranged for preventing an image shake resulting from the vibrations of hands holding a camera in taking pictures by detecting the vibrating state of the camera with vibration detecting means and shifting a correction lens in the direction perpendicular to an optical axis according to the result of vibration detection.
The camera having such an image-shake correcting device is arranged to movably hold the correction lens, which constitutes at least a part of a photo-taking lens system. Shaking of images is canceled by moving the correction lens within a plane perpendicular to the optical axis of a main optical system in such a direction as to absorb the image shake.
In the image-shake correcting device, a coil and a magnet are arranged to constitute an electromagnetic actuator with one of them mounted on a fixed part and the other on a lens holding frame which holds the correction lens. The image-shake correcting device is thus arranged to directly move the lens holding frame. It is advantageous, in respect of reduction in size and saving of electric energy, to mount the magnet, which is heavier in weight, on the fixed part and the coil, which is lighter in weight, on the lens holding frame. Accordingly, the electric wiring is arranged with a flexible printed circuit board from the fixed part to the coil mounted on the lens holding frame.
Further, in order to accurately move the lens holding frame with respect to the fixed part within the plane perpendicular to the optical axis, three pins are arranged at equal spaces in the circumferential direction on one of the lens holding frame and the fixed part, while three corresponding slots are formed to respectively extend in the circumferential direction in the other of the lens holding frame and the fixed part. The lens holding frame is thus arranged to move in the direction perpendicular to the optical axis while the pins are in a state of respectively abutting on the end faces in the optical axis direction of the slots.
However, the required rates of precision for machining and positioning tend to be increased by attempts to reduce the size of the whole optical system and to adapt the optical system to a zoom lens of high magnification. Then, the optical performance required cannot be satisfied if there is even a slight deviation from a perfect state. To prevent the optical performance from being degraded by play between the pins and slots, the clearance between the pins and slots must be minimized. On the other hand, in order to ensure smooth movement even under a high or low temperature condition, it is necessary to have a predetermined amount of clearance between the pins and slots. In other words, it is a prerequisite to the accurate image-shake correction to eliminate the play while keeping smooth movement of the lens holding frame.
Therefore, it has been developed to eliminate the play by urging the lens holding frame in the optical axis direction with a coiled spring in such a way as to push each of the pins against one end face in the optical axis direction of the corresponding slot.
However, if the lens holding frame is urged in the optical axis direction by means of the coiled spring, the sliding friction between the coiled spring and the lens holding frame increases. Then, the increased friction increases a loss of a driving force to make it hardly possible to correct a minute image shake. Further, even in a case where the optical performance is sufficient for permitting a slight amount of play and making the urging by means of the coiled spring unnecessary, a problem arises in that, in the case of a video camera, an operation sound due to the play or the sliding motion would be recorded during process of an image-shake correcting action.
Another problem of the conventional image-shake correcting device lies in the heavy weight of the lens holding frame which holds the correction lens. The heavy weight of the lens holding frame necessitates a large amount of current to be applied to the coil, for keeping the lens holding frame in a vertically buoyant state, against electric energy saving efforts in the cameras or the like.